US2367660A - Process of photopolymerization - Google Patents

Description

Patented Jan. 23, 1945 raoccss or PHOTOPOLYMERIZATION Courtland L. Agre, Minneapolis, Minn., asslgnor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation oi. Delaware .kNo Drawing.

Application December 31, 1941, Serial No. 425,201

1!? Claims. (Cl. 204158) This invention relates to the photopolymerization of polymerizable ethylenically unsaturated organic compounds, 1. e., the polymerization thereof under the influence of light.

The photopolymerization of certain ethylenically unsaturated compounds has long been known, but the rate of polymerization has hitherto been such that photopolymerization has not recommended itself as a feasible method for polymerization on the commercial scale largely because of the slowness of the process.

This invention has as an object an improvement in the photopolymerization of a photopolymerizable ethylenically unsaturated organic compound having a methylene (CH2) group attached by a double bond to a carbon which is in turn attached to a carbon all of the remaining valences of which are satisfied through polyvalent electronegative inorganic elements of the first full period of the periodic system, which comprises eiiectin the photopolymerization of said compound in the presence of, i. e., admixed with a vicinal ketaldonyl compound, i. e., a compound having a plurality of vicinal carbonyl groups wherein the terminal valences are satisfied by hydrogen or monovalent hydrocarbon radicals and :c is two or three, and preferably two.

The photopolymerizable ethylenically unsaturated compounds of this invention have a methylene (CH2) group attached by a double bond to a carbon which is in turn attached to a carbon all of the remaining valences of which are satisfied through polyvalent electronegative inorganic elements of the first full period of the periodic system. They include the acids, esters, amides, and nitriles of acrylic, alpha-halogen substituted acrylic and alpha hydrocarbon substituted acrylic acids, i. e., compounds having the structure where X is hydrogen, halogen, or hydrocarbon and Y is COOR, CONHz, or CN, and R is hydrogen or hydrocarbon.

The photopolymerization may be according to any of the modes known to the art, e. g., bulk,

and the solution is placed in a suitable vessel. The vessel can be constructed or glass so that the light can enter the system through the sides of the vessel, or there can be a source of light within the vessel. The source of light may be sunlight, a mercury vapor lamp, a tungsten bulb, or some similar arrangement to give light either in the range of the ultraviolet rays plus visible light, or in the range of visible light alone. Polymerization occurs fairly rapidly under relatively mild conditions of temperature; and the rate is dependent on the temperature in the system and the intensity of the light. In order to obtain sheets and castings free from defects, it is desirable to control the temperature so that local over-heating does not occur. The extent of polymerization can be determined by measuring the refractive indexwhich changes with the degree of polymerization or by gravlmetric methods involving the separation of the polymeric product. By application of this process, bulk castings free from surface defects can be obtained in a relatively short period of time.

In emulsion polymerization the readily polymerizable ethylenic compounds and photopolymerization catalysts (vicinal polyketaldonyl compounds) are held in emulsion in water by an emulsifying agent. The emulsion is'then irradiated through the side of the vessel or by some other suitable method until polymerization has proceeded to the desired extent. Still more rapid polymerization occurs if a peroxide (such as hydrogen peroxide) is present in the emulsion together with the vicinal polyketaldonyl compound. The polymer is then precipitated from the emulsion, after the removal of residual monomer, by the addition of a small amount of an electrolyte or by freezing. The product is then thoroughly washed and dried in the usual manner.

In the granular process of polymerization, the

material to be polymerized containing a.small amount of the vicinal polyketaldonyl compound as the photopolymerization catalyst is rapidly agitated in an aqueous system containing a small percentage (up to about 3%) of a protective colloid, which acts as the granulating agent, in a vessel equipped with a reflux condenser at such a temperature that moderate reflux is maintained. Under these conditions the material undergoing polymerization is dispersed in the form of small droplets which solidify as polymerization proceeds to give a polymer in the form of small granules. The granules are readily filtered from the mixture, washed free from occluded colloid-and dried.

In the solution method, the ethylenic compound and the polyketaldonyl compound are dissolvediin a solvent and light is directed upon the solution until the desired extent of polymerization is achieved.

The more detailed practice of the invention is Example I This example illustrates the bulk photopolymerization of methyl methacrylate in the presence of vicinal polyketaldonyl compounds.

Methyl methacrylate specimens containing one per cent of their weight of the polyketaldonyl compound indicated in the table below were placed in glass vessels and were exposed at 40 C. to the light from a mercury vapor light (a Westinghouse H-3 lamp modified by mounting the bulb in a 20 mm. quartz tube) operating at 85 watts and mounted at a distance of 6 inches from the specimens. The indicated time represents the period required for the liquid monomer to be converted into a solid (about 30%) polymer. For example, the sample which contained diacetyl solidified in 2 hours, whereas a control specimen containing no photopolymerization catalyst solidified in 12 hours. The following table lists the observed data.

Example If This example illustrates the effect of the concentration of the vicinal polycarbonyl compound on the rate of photopolymerization of methyl methacrylate in bulk at 40 C.

A series of methyl methacrylate samples containing 0.001, 0.01, 0.1 and 1.0% of diacetyl was prepared and placed in glass vessels. The

' aaemoo presence or photopolymerization catalysts under various conditions. The present example illustrates the eflect of diacetyl on the photopolymerization ofvarious monomers. The time element as noted in the table below represents the period in hours required for polymerization of the listed monomer to a solid and in each instance is compared with'the period necessary for similar polymerization of a control having no photopolymerization catalyst present.

The material to be polymerized was placed in a glass vessel (capable of transmitting light of greater than 2850 A.) and 0.1% of diacetyl was samples were then irradiated with light from a 6 inch mercury vapor are operating at about 150 volts, and 4.5 amperes mounted at a distance of lO-l2 inches and the extent of polymerization measured by means of the refractive indices as polymerization proceeded. The following table indicates the time required to effect 5% polymerization of methyl methacrylate monomer in the presence of the designated amount of photopolymerization catalyst.

tion

Time for 5% t Example III The previous examples illustrate the photopolymerization of methyl methacrylate in the added. The solution was then exposed at 40 C.

to the light from a mercury vapor are as in Example II at a distance of 10-12 inches until the material had become solid. In each instance a control without diacetyl was irradiated simultaneously.

( means greater than; means less than).

Example IV This example illustrates the preparation of a sheet Casting'by the process 01 this invention.

A solution of about 0.1% pentanedione-2,3 in methyl methacrylate in a Pyrex" glass vessel was irradiated by means of a mercury vapor are as in Example II at a distance of 8-10 inches until a thin syrup had formed. This syrup was then poured between two sheets of glass plate which were separated by a flexible separator. The sample was then placed on a ground glass plate mounted at an angle of about 5 from horizontal, and pressure was uniformly applied on the plates. Irradiation was provided from below by means of a mercury vapor lamp of the type described in Example I at a distance of about 10-12 inches, and was continued at about room temperature until polymerization was practically complete. When the restraining glass plates were removed by soaking in warm water, there was obtained a cast sheet of the polymer which is free from visible defects such as bubbles, striations, discoloration and the like.

Example V This example illustrates the Preparation of a large hulk casting by the practice of this invention.

A solution of methyl methacrylate containing about 0.1% of 2,2-dimethyli-phenylbutanedione-3,4 was placed in a suitable glass container which was mounted in a fluid to provide a means for controlling the temperature of polymerization. Light from a mercury lamp as described in Example I was directed through the bottom of the container at a distance of 6-8 inches until polymerization appeared to be practically complete. The bulk casting was then baked several hours at about 75 C. to insure complete polymerization. The product thus obtained was practically colorless and is free from defects such as bubbles, striations, and the liige.

.time of irradiation.

Example VI 140 parts of methyl methacrylate, 260 parts of distilled water and 8 parts of an emulsifying agent (the sodium salt of the sulfate of oleyl alcohol) was added to each of three Pyrex glass vessels. of diacetyl was added. Two of these tubes were exposed at C. to the irradiation of a mercury vapor lamp, as described in Example I, at a distance of 6-8 inches, while the other was kept in the dark at the same temperature. At the end of 80 minutes all the emulsions were broken by the addition of an electrolyte (aluminum sulfate) and the polymers were isolated. The following table contains the data thus obtained, and shows the beneficial efiect of the presence of diacetyl in the photopolymerization of methyl -methacrylate.

Example VII This example illustrates the emulsion photopolymerization of methyl methacrylate under the influence of a peroxide and a vicinal polyketaldonyl compound with only a very short initial irradiation, the polymerization continuing even in the dark.

fifteen parts of an emulsion prepared from 150 parts of redistilled methyl methacrylate, 291 parts of distilled water, and 9 parts of an emulsifying agent (sodium salt of the sulfate of oleyl alcohol) was added to each of a series of Pyrex glass receptacles. To certain of these samples 0.025 part of diacetyl was added, to others 0.075 part of 35% hydrogen peroxide solution was added, while to others either both or none of these two materials were added as indicated in the following table. The samples were then exposed at 35 C. to the irradiation of a mercury vapor lamp, as described in ExampleI, at a distance of 6-8 inches for the length of time indicated in the table under The samples were removed at the designated time and were kept in the dark and were precipitated after elapsev of the time represented in the table by time of precipitation. This time represents the period elapsed between the start of irradiation and the precipitation of the sample; the difference between the time of precipitation and time of irradi ation represents the time that the samples remained in the dark after irradiation and before precipitation.

These data indicate that irradiation of the emulsion itself with hydrogen peroxide but with To two of these containers, 0.035 part no diacetyl caused no substantial polymerization, while the irradiation in the presence of diacetyl, with or without hydrogen peroxide, caused considerable polymerization, and finally that the sample having both diacetyl and peroxide which was only momentarily irradiated polymerized practically completely after standing in the dark for about 1 hours.

Example VIII The following example illustrates the simultaneous photopolymerization of methyl methacrylate and other unsaturated polymerizable materials by the emulsion process-in the presence of a peroxide and of a polyketaldonyl compound.

One hundred parts of a solution prepared from 52.2 parts of an emulsifying agent (the sodium salt of the sulfonate formed in the reaction of sulfur dioxide and chlorine on white oil by the process of U. S. Patent 2,197,800), 548 parts of distilled water, 9.6 parts of hydrogen peroxide (35%), and 3.0 parts of diacetyl dissolved in 30 parts of water, 44 parts of redistilled vinyl chloride, and 6 parts of methyl methacrylate are placed in a Pyrex glass tube which was then sealed and irradiated for 18 hours at a distance of about 6 inches fromv a mercury vapor lamp, as described in Example I, submerged in water maintained at 40 C. At the end of this time the tube was removed from the water bath, the .contents were frozen and the tube was opened. The product was then thoroughly steam distilled, was washed several times in hot water, and finally was washed with alcohol. The dry product thus obtained amounted to 48 parts, corresponding to a yield of 96%.

The following table represents-data obtained from polymers prepared in the same way from vinyl chloride or vinylidene chloride with the designated monomer A. The polymers were formed under conditions analogous to those of the above description.

M rinomer A Parts Monomer B Parts P a};

Acrylonitrile Methyl alpha-chlo r acrylate. Acrylonitrile Methyl methacrylate.

Vinyl chloride. ..do

Vinylidene chloride. 5 do,

p yeast Example IX The following example illustrates the beneficial effect of the presence of. a polyketaldonyl compound on the photopolymerization of methyl methacrylate in solution.

A solution of 100 parts of methyl methacrylate in 200 parts of acetone was divided into two parts and to one was added 0.1 part of diacetyl. The two solutions were then exposed simultaneously in Pyrex containers to the light from a mercury vapor arc, as describec'l'in Example II; at a distance of 8-10 inches. After irradiation for 6 hours, the polymers were precipitated from the solution. The following yields were obtained: Polymerization with diacetyl, 63.4%; polymerization without diacetyl, 30.8%.-

Example X This example illustrates the application of this invention to the granular photopolymerization of methyl methacrylate.

A mixture of 200 parts of water, 1 part ,of methyl starch (granulating agent), 100 parts of methyl methacrylate, and 0.5 part of diacetyl was placed in a vessel or such construction that its contents could be irradiated by means of a mercury vapor are, as described in Example II, at a distance of 6-7 inches. The mixture was stirred vigorously and was heated under reflux. In 55 minute polymerization was practically complete. The granular product was washed well and dried, giving an almost quantitative yield of. polymer. The material was molded into a chip which softened at about 123 C.

Example XI This example illustrates the use of sunlight in the photopolymerization of methyl methacrylate with the aid of a photopolymerization catalyst.

Three hundred grams of methyl methacrylate monomer, 0.3 gram of diacetyl and 0.42 gram of lauroyl peroxide were placed in a glass vessel and irradiated for 3 hours with a Westinghouse H-B mercury vapor lamp. The product at this stage was a viscoussyrup with a viscosity of 36 poises and a polymer content of 14%.

One hundred and twenty grams of the above syrup was poured into a cell which consisted of two sheets of plate glass separated by a flexible "ThiokoP gasket. The polymerization mixture was then exposed to sunlight for 2 hours and subsequently was heated in an oven at 100 C. for 2 hours. The resulting sheet was clear, tough, and

transparent, and bubble-free.

Example XII This example illustrates the use of a tungsten light in the catalysed photopolymerization of meth l methacrylate.

One hundred and twenty grams of the 14% polymer syrup as prepared in the above example was poured into a cell consisting of two sheets of plate glass separated by a flexible Thiokol asket and was then irradiated for 2% hours with a General Electric Mazda, 98-52-1500 watt, 110 volt bulb at a distance of 2 feet. After the irradiation the polymer was subjected to a heat treatment for 2 hours at 100 C. A clear, transparent, bubble-free sheet was obtained.

In the process of this invention there may be employed any vicinal polyketaldonyl compound of the formula R-(COb-R wherein a is an integer of two or three, and preferably two, and R and R are hydrogen or monovalent hydrocarhon radicals. Illustrative polyketaldonyl compounds include diacetyl, pentandione-2,3, octandione-2,3, l-phenylbutandione-LZ, benzil, 2,2-dimethyl-i-phenylbutandione-3,4, glyoxal, phenylglyoxal, diphenyltriketone, and cyclohexanedione.

The invention is generic to the use of any such vicinal polyketaldonyl compounds in the photopolymerization, including photointerpolymerization, of an ethylenically unsaturated compound having a methylene (CI-I2) group attached by a double bond to a carbon which is in turn attached to a carbon all of the remaining valences of which are satisfied through polyvalent electronegative inorganic elements of the first full period of the periodic system, which compound may be photopolymerized either alone or at least in combination with another such compound. Illustrative compounds include acrylic, chloroacrylic, and methacrylic esters, amides, nitriles, e. g., methyl acrylate, methyl chloroacrylate, methyl methacrylate, methacrylamide, methacrylonitrile, and acrylonitrile. Alkyl acrylates and methacrylates, particularly lower (1-4 car-- bon) alkyl acrylates and methacrylates are particularly preferred because of the rapidity, convenience and satisfactory nature of their photoolymerization. The acrylates and methacrylates are esters of aliphatic monocarboxylic acids of from 3 to 4 carbons having the carboxyl attached to a monovalent hydrocarbon radical having an ethylenic double bond between the carbon attached to the carboxyl and a carbon once'removed therefrom.

Th invention is also applicable to mixtures which photopolymerize. Thus certain unsaturated compounds which do not polymerize readily alone under the influence 01 light will polymerize simultaneously with other readily polymerizable materialsj these' unsaturated compounds also are included in this invention. An example is the simultaneous polymerization of diethyl iumarate, which does not polymerize readily, and methyl methacrylate which polymerizes easily. Unsaturated materials which do not polymerize under the action of light alone or at least in mixture with other photopolymenzable ethylenically unsaturated compounds are excluded from this invention.

The present invention is an improvement in photopolymerization, i. e., in polymerization inii-uenced by radiant energy in the form of light rays, both visible and invisible. The term light as herein used includes wavelengths both in the infrared and in the ultraviolet and, of course, wavelengths of all light in the intermediate visible spectrum. Light waves in the infrared are operable in eilecting photopolymerization of the compounds herein described in the presence of the designated photopolymerization catalysts but the rate of photopolymerization is slower than in visible or in ultraviolet light. Light in the ultraviolet region having wavelengths shorter than 3200 Angstroms and, for example, down to 1800 Angstroms which is the limit of transmission of quartz is operable in this process. The most useful and effective light is that having wavelengths between 3200 Angstroms and 7000 Angstroms. Although as pointed out above, wavelengths below 3200 Angstroms are effective, no difference in the rate of polymerization is noted when wavelengths of light of equal intensity and lower than 3200 Angstroms are prevented from reaching the photopolymerizable compound. Thirty-two hundred Angstroms is the lower limit of transmission of ordinary glass and since light passing through this material is frequently used in this process, this figure represents a lower preferred limit. The upper limit of 7000 Angstroms represents the beginnin of the infrared band having the less effective wavelengths.

The wavelengths of light actually utilized in the photopolymerization process depend frequently on the opacity or transparency of the walls of the container holding the photopolymerizable compound. In general, light which contains wavelengths higher than those to which the transparent material is partially or completely opaque is necessary. For example. when ordinary glass is used as a container for the photopolymerizable material, and light is transmitted through the walls of the container, the light reaching the photopolymerization reaction mixture is largely that containing wavelengths greater than 3200 Angstroms. When tubes or vessels of Pyrex glass are employed to hold the photopolymerization reaction mixture, the lower limit. of the light available is approximately 2850 angstroms. The limit of actinic rays for methyl methacrylate itself is about 3500 Angstrom, so that in photopolymerizations using methyl methacrylate monomer, light havinga wavelength greater than 3500 Angstroms should, in general, be available for the photopolymerization. In a polymerization of this type, the walls of the container are not always a limiting factor since it has been shown that X-rays of wavelengths of 0.7 Angstrom are also effective for causing polymerization.

It is advantageous to use such a system that a controlled amount of light comes into contact with the material to be photopolymerized. The rate of the photopolymerization varies directly with the intensity of the light and can usually be increased or diminished b increasing or diminishing the intensity of the light that reaches the reaction mixture. A convenient source of light of proper intensity is the mercury vapor are which emits light in the ultraviolet as well as in the visible range. Another convenient source of light is a tungsten bulb of suitable intensity, for example, a General Electric Mazda PS-52, 1500 watt, 110 volts, will function effectively. Sunlight is another source of effective light for carrying out the photopolymerization in the presence of the photopolymerization catalysts.

Difiused daylight contains wavelengths of light which are active for the catalyzed photopolymerization but the reaction is considerably slower than with other more intense sources of light.

The type of container used for the polymerization depends upon the results desired. For instance, in the bulk polymerization of a monomer to form sheeting, it is desirable to have smooth surfaces; and, consequently, glass plates ordinarily are used. In small scale granulation and emulsion polymerization Pyrex glass containers may be employed. However, in industrial applications such containers would not be available in sumciently large size and it is necessary to use metallic containers with the light above or within the material to be polymerized.

The temperature of polymerization is dependent on the monomer being polymerized and the type of process employed. The usual range is from room temperature to about 100 C. In the bulk polymerization of a material such as methyl methacrylate it is necessary to keep the temperature fairly constant at some value within the range of 25 to 85 C. in order to control the polymerization and avoid the development of defacts. The molecular weight is somewhat dependent upon the temperature of polymerization as well as on other factors, and this consideration therefore enters into the determination of operating conditions. Granualr polymerization ordinarily is carried out at reflux temperature; emulsion polymerization at about 25-85 C. Temperatures above 100 C. can frequently'be advantageously employed in apparatus designed to withstand the operating pressure. I

The concentration of polyketaldonyl compound in the solution is of importance because-it appreciably affects the rate of polymerization, as shown in Example 2. From 0.5 to 0.2% of the vicinal polyketaldonyl compound, based on the photopolymerizable compound, is preferred. Usually about 0.1% of a vicinal polyketaldonyl compound is employed, although either more or less, i. e., as little as 0.01% or as much as 1.0%, can be used depending upon the nature of the product being prepared and on the rate of polymerization desired. Furthermore, the photopolymerization catalyst need not; be employed alone in the photopolymerization iof the readily polymerizable materials, but can be used in conjunction with a peroxide. Thus, in bulk polymerization, the presence of both benzoyl peroxide and a vicinal polyketaldonyl compound causes more rapid polymerization than in the instances in which the polyketaldonyl compound is present alone. Furthermore, in a system of this type, a monomer which is only partially polymerized when irradiation is discontinued will continue to polymerize at a fairly rapid rate at elevated temperatures. Similarly, in both,.granular and emulsion systems it often is desirable to use both a vicinal polycarbonyl compound and a peroxide for most advantageous results. Usually photopolymerization with light and a peroxide occurs slowly, while the addition of a small amount of a vicinal polyketaldonyl compound to such-a system greatly increases the polymerization rate.

Benzoyl peroxide, acetyl benzoyl peroxide, di-

tion catalysts and light. The molecular weight of the polymer also is appreciably dependent on the concentration of the photopolymerization catalyst in the system.

The nature of the gaseous atmosphere above the sample in the vessel is of importance. Experiments have indicated that an atmosphere of oxygen practically stops polymerization, whereas an atmosphere of nitrogen gives the greatest amount of polymerization within a definite period of time. Consequently, although air it-' self is usually employed as the atmosphere above the sample and ordinarily is quite satisfactory, polymerization will proceed at a greater rate when the oxygen in the air is at least partially removed.

In granular and emulsion systems it is occasionally desirable to control the pH values. In the emulsion polymerization of methyl methacrylate with vinyl or vinylidene chloride, it is desirable to operate at a pH of about 2.5. In such cases the original emulsifying systems are adjusted to this pH by the addition of an acid such as formic acid or other strong acids. These factors are dependent on the systems and monomers being polymerized.

Emulsifying or dispersing agents selected must be suitable for use in the system employed. Dispersing agents which perform acceptably in acid media include salts of sulfonic acid and sulfuric acid esters of long chain compounds, such as the sodium salt of acetoxyoctadecanesulfate. This invention is not limited to the application of any specific emulsifying agents. Furthermore, in. the granular method of polymerization the protective colloids used as granulating agents can be any type of soluble starch, methylated starch, partially hydrolyzed polyvinyl acetate, the sodium salts of polymers or interpolymers containing acrylic or methacrylic acids, polymethacrylamide,

- sodium starch glycolate, sodium cellulose glylight of appropriate wavelength and intensity through-the transparent member. This improvement is described in greater detail in application Serial No. 425,187, filed of even date herewith, by Robert E. Christ.

The nature of the products obtained by the practice of this invention is entirely dependent upon the materials which are polymerized and, consequently, vary widely in their properties. Since the properties of the products obtained by the application of this invention are analogous to similar products obtained by other processes of polymerization of the same materials, the products can be used in any way that the polymers regularly obtained are used. Consequently, no attempt is made to limit the use of the materials. Potential uses are in molding compositions, in coating and impregnating fabrics, paper, and

leather, in adhesives, in safety glass interlayers,

and in similar applications.

The term ketaldonyl has been applied to designate the 0 group as it appears in aldehydes and ketones in contradistinction to the 0:0 group as it appears in acids or esters. The CO group as it appears in acids R-CO-OH or esters R-COOR is very different in its properties from the carbonyl group in aldehydes and ketones and the expression ketaldonyl group is employed to distinguish th aldehydic and ketonic carbonyl group from the acidic CO group, i. e., to distinguish the CO-- group whose remaining valences are satisfied by hydrogen or carbon from the acidic -CO- group at least one of the valences of which is satisfied by hydroxyl, halogen, amido or like negative group. The term ketaldone is used as a ge neric designation for aldehydes and ketones.

The above description and examples are intended to be illustrative only. Any modification of or variation therefrom which conforms to the spirit of the invention is intended to be included within the scope of the claims.

What is claimed is:

1. Process for preparing polymers which comprises irradiating, with light of wavelengths in the range of 1800 to 7000 Angstroms of such intensity and for a time sufficient to produce a substantial amount of polymerization, a composition comprising a photopolymerizable compound of the formula wherein X is selected from the class consisting of hydrogen, halogen, and hydrocarbon and Y is selected from the class consisting of the esterified x on -o wherein X is selected from the class consisting of hydrogen, halogen, and hydrocarbon and Y is selected from the class consisting of the esterified carboxyl group, the carbon-amido group,

and the nitrile group and, as a photopolymerization accelerator therefor, a compound of the formula wherein X is selected from the class consisting oi hydrogen, halogen, and hydrocarbon and Y is selected from the class consisting of the esterified carboxyl group, the carbon-amido group, and the nitrile group and, as a photopolymerization as accelerator therefor, acompound of the formula nF-co-co-a' wherein R and R. are selected from the class consisting of hydrogen and monovalent hydrogg carbon radicals.

4. Process for preparin polymers which comprises irradiating, with light of wavelengths in the range of 1800 to 7000 Angstroms of such intensity and for a time sufiicient to produce a substantial amount of polymerization, a composition comprising a photopolymerizable compound of the formula CHFC\ wherein X is selected from the class consisting of hydrogen, halogen, and hydrocarbon and Y is selected from the class consisting of the esterifled carboxyl group, the carbon-amide group,

and the nitrile group and, as a photopolymerization accelerator therefor, a compound of the formula a-co-co-n' wherein X is selected from the class consisting of hydrogen, halogen, and hydrocarbon and Y is selected from the class consisting of the esterified carboxyl group, the carbon-amido group, and the nitrile group and, as a photopolymerization accelerator therefor, diacetyl.

6. Process for preparing polymers which comprises irradiating, with light of wavelengths in the range of 1800 to 7000 Angstroms of such intensity and for a time sufllcient to produce a substantial amount of polymerization, a composition comprising methyl methacrylate and, as a photopolymerization catalyst therefor, a vicinal polyketaldonyl compound.

7. Process for preparing polymers which comprises irradiating, with light of wavelengths in the rangeof 1800 to 7000 Angstroms of such intensity and for a time sufficient to produce a substantial amount of polymerization, a composition comprising an alkyl ester of an acyclic monocarboxylic acid wherein the carboxyl is attached to a hydrocarbon radical of from two to three carbon atoms wherein the carbon attached to the carboxyl group is attached-by an ethylenic double bond to a methylene (CH2) group and, as a photopolymerization catalyst therefor, a vicinal polyketaldonyl compound.

8. Process of claim '7 wherein the ester polymerized is an ester of a one to four carbon alkanol.

9. Process for preparing polymers which comprises irradiating, with light of wavelengths in the range of 1800 to '7000 Angstrom of such intensity and for a time sufilcient to produce a substantial amount of polymerization, a composition comprising methyl methacrylate and, as a photopolymerization catalyst therefor, diacetyl.

10. Process for preparing polymers which comprises irradiating, with light of wavelengths in the range of 1800 to 7000 Angstroms of such intensity and for a time sufficient to produce a substantial amount of polymerization, a composition comprising an alkyl ester of an acyclic monocarboxylic acid wherein the carboxyl is attached to a hydrocarbon radical of from two to three carbon atoms wherein the carbon attached to the carboxyl group is attached by an ethylenic double bond to a methylene (CH2) group and, as a photopolymerization catalyst therefor, diacetyl.

11. Process for preparing polymers which comprises irradiating, with the light generated by a mercury vapor lamp having wavelengths in the range of 3200 to'7000 Angstroms of such intensity and for a time sufilcient to produce a substantial amount of polymerization, a composition comprising a photopolymerizablecompound of the formula wherein X is selected from the class consisting of hydrogen, halogen, and hydrocarbon and Y is selected from the class consisting of the esterifled carboxyl group, the carbon-amido group, and the nitrile group and, as a photopolymerization accelerator therefor, a vicinal polyketaldonyl compound.

12. Process for preparing polymers which comprises irradiating, with the light generated by a mercury vapor lamp having wavelengths in the range of 3200 to 7000 Angstroms of such intensity and for a time sufficient to produce a substantial amount of polymerization, a composition comprising methyl methacrylate and diacetyl.

13. Process for preparing polymers which comprises irradiating, with light of wavelengths in the range of 1800 to 7000 Angstroms of such intensity and for a time sumcient to produce a substantial amount of polymerization. a composition comprising a photopolymerizable compound of the formula wherein K is selected from the class consisting of hydrogen, halogen, and hydrocarbon and Y is selected from the class consisting of the esterifled carboxyl group, the carbonamide group, and the nitrile group and, as'a photopolymerization accelerator therefor, a compound of the formula wherein R and R are hydrocarbon radicals.

14. Process for preparing polymers which comprises irradiating, with light of wavelengths in the range of 1800 to 7000 Angstroms or such in-- wherein R and R are hydrocarbon radicals.

15. Process for preparing polymers which comprises irradlating, with light of wavelengths in the range of 1000 to 7000 Angstroms of such intensity and for a time sufliclent to produce a substantial' amount of polymerization, a composition comprising methyl methacrylate and, as a photopolymerization catalyst therefor, a compound of the formula R-CO-CO-R' wherein R and R' are hydrocarbon radicals.

17. Process for preparing polymers which comprises irradiating, with light or wavelengths in the range of 1000 to 7000 Angstroms of such intensity and for a time sufllclent to produce a substantial amount of polymerization, a composition comprising acrylonitrile and, as a photopolymerization catalyst therefor, diacetyl.

18. Process for preparing polymers which com.

prises irradiating, with light of wavelengths in the range of 1800 to 7000 Angstroms of such intensity and for a time sumcient to produce a substantial amount of polymerization, a composition comprising an alkyl ester of an acyclic monocarboxyllo acid wherem the carboxyl is attached to a hydrocarbon radical of from two to three carbon atoms wherein the carbon attached to the carboxyl group is attached by an ethylenlc double bond to a methylene (CH2) group and, as a photopolymerization catalyst therefor, behlil.

19. Process for preparing polymers which oomprises irradiating, with light of wavelengths in the range of 1800 to 7000 Angstrom of such intensity and for a time sufficient to prod a substantlal amount of polymerisation, a composition comprising methyl methacrylate and, as e photopolymerization catalyst therefor benlil;

OOUBTLAND L. AGRI.